1. Field of the Invention
The present invention relates to a rotation speed detection circuit of a motor for drive control of the motor and a motor driver apparatus (including a pre-driver) having the same, and particularly to a motor driver apparatus having a phase control function and a speed servo circuit.
2. Description of Related Art
In general, in drive control of a brushless motor or the like, a lag may occur in a phase of a drive signal and cause a decrease of drive efficiency in accordance with rotation speed of the motor. Therefore, control of increasing motor output torque (so-called lead angle control) is usually performed, in which a phase of the drive signal to be supplied to a motor coil is intentionally set to lead a phase of a Hall signal detected by a Hall sensor.
There are conventional methods of the lead angle control described in JP-A-2002-199778, JP-A-2004-48951 and JP-A-2008-154385, for example, in which a voltage generated in a resistor for sensing phase current is detected for controlling so that zero-cross timing of induction voltage (i.e., electromotive force) of a motor coil and a phase of the phase current are substantially equal to each other, or the voltage generated in the phase current sensing resistor is detected and smoothed for performing the lead angle control in proportion to the phase current.
However, these methods utilize the phase current sensing resistor. Therefore, they can easily be affected by switching noise and have other problems such as that stable control cannot be performed.